Film Cooling Characteristics of a High Lift Blade Including Tip and Platform Flow Interactions

Abstract

This paper investigates the aerodynamic and film cooling characteristics of a first stage turbine high lift blade. The blade operating conditions are representative of those normally found in a heavy-duty gas turbine. The airfoil incorporates several rows of film cooling holes located at various axial positions along the airfoil chord and the blade tip. Additionally the impact of the platform leading edge rim purge flow has been investigated and its interaction with the airfoil aerodynamic and film cooling characteristics. The film cooling holes are geometrically three-dimensional in shape, and depending on the location on the airfoil, they consist of various fan shapes, which are either compounded or in-line with the external main flow direction. Numerical studies and experimental investigations in a linear cascade have been conducted for a range of exit Mach and Reynolds numbers. The influence and sensitivity of the coolant ejected from the airfoil, tip and the platform rim purges on the overall airfoil film cooling has been investigated for a range of operating conditions. The measured film cooling effectiveness on the airfoil, blade tip and platform surfaces compared well with the predictions. The suction side film cooling effectiveness, which consisted of two pre-throat film rows, proved to be very effective up to the suction side trailing edge. The impact of variations in the airfoil cooling flows showed that the film cooling was relatively in-sensitive on the suction side. However, on the blade tip, it was found that the film cooling characteristics are strongly dependent on the clearances and the tip coolant ejection rate. On the platform surface, the impact of variations in the rim purge flows was evident, but proved not to alter the global film cooling characteristics on neither the airfoil nor the platform surfaces significantly.